Creé unNSOperationQueue para descargar imágenes (desde Twitter para celular):

NSOperationQueue *queue = [[NSOperationQueue alloc]init];
   [queue addOperationWithBlock:^{
    NSString *ImagesUrl = [[NSString alloc]initWithFormat:@"http://api.twitter.com/1/users/profile_image/%@",[[status objectForKey:@"user"]objectForKey:@"screen_name"]];;
        NSURL *imageurl = [NSURL URLWithString:ImagesUrl];
        UIImage *img = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageurl]];
        [[NSOperationQueue mainQueue]addOperationWithBlock:^{
            if (img.size.width == 0 || [ImagesUrl isEqualToString:@"<null>"]) {
                [statusCell.imageCellTL setFrame:CGRectZero];
                statusCell.imageCellTL.image = [UIImage imageNamed:@"Placeholder"] ;
            }else

            [statusCell.imageCellTL setImage:img];

esto funciona bien, pero cuando aparece para mover el desplazamiento y ver las imágenes aún se están cargando, y cambian varias veces hasta que se obtiene una imagen.

Y no me gusta el perfil de diagnóstico del tiempo, así que quería hacer esto de alguna maneraNSOperationQueue en el fondo

También es posible mostrar cómo hacer un "Imagecache" sin necesidad de descargar una imagen ya descargada.

** (Estado = NSDiccionario de la línea de tiempo de Twitter).

edición: :( todas las celdas)

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{


    static NSString *CellIdentifier = @"Celulatime";
    UITableViewCell *Cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier];


    if ( [Cell isKindOfClass:[TimeLineCell class]] ) {
        TimeLineCell *statusCell = (TimeLineCell *) Cell;
        status = [self.dataSource objectAtIndex:indexPath.row];


        statusCell.TextCellTL.text = [status objectForKey:@"text"];
        statusCell.NomeCellTL.text = [status valueForKeyPath:@"user.name"];
        statusCell.UserCellTL.text = [NSString stringWithFormat:@"@%@", [status valueForKeyPath:@"user.screen_name"]];


        NSDate *created_at = [status valueForKey:@"created_at"];
        if ( [created_at isKindOfClass:[NSDate class] ] ) {
            NSTimeInterval timeInterval = [created_at timeIntervalSinceNow];
            statusCell.timeCellTL.text = [self timeIntervalStringOf:timeInterval];
        } else if ( [created_at isKindOfClass:[NSString class]] ) {
            NSDate *date = [self.twitterDateFormatter dateFromString: (NSString *) created_at];
            NSTimeInterval timeInterval = [date timeIntervalSinceNow];
            statusCell.timeCellTL.text = [self timeIntervalStringOf:timeInterval];
        }

        NSString *imageUrlString = [[NSString alloc]initWithFormat:@"http://api.twitter.com/1/users/profile_image/%@",[[status objectForKey:@"user"]objectForKey:@"screen_name"]];;
        UIImage *imageFromCache = [self.imageCache objectForKey:imageUrlString];

        if (imageFromCache) {
            statusCell.imageCellTL.image = imageFromCache;
            [statusCell.imageCellTL setFrame:CGRectMake(9, 6, 40, 40)]; 
        }
        else
        {
            statusCell.imageCellTL.image = [UIImage imageNamed:@"TweHitLogo57"];
            [statusCell.imageCellTL setFrame:CGRectZero]; 

            [self.imageluckluck addOperationWithBlock:^{
                NSURL *imageurl = [NSURL URLWithString:imageUrlString];
                UIImage *img = [UIImage imageWithData:[NSData dataWithContentsOfURL:imageurl]];

                if (img != nil) {


                    [self.imageCache setObject:img forKey:imageUrlString];

                    // now update UI in main queue
                    [[NSOperationQueue mainQueue] addOperationWithBlock:^{

                        TimeLineCell *updateCell = (TimeLineCell *)[tableView cellForRowAtIndexPath:indexPath];

                        if (updateCell) {
                            [updateCell.imageCellTL setFrame:CGRectMake(9, 6, 40, 40)]; 
                            [updateCell.imageCellTL setImage:img];
                        }
                    }];
                }
            }];
        }


        }
    return Cell;
    }